Two stages, but either element can start to fail in the open position, this allows the short circuit of coolant from the radiator and into the coolant flow.

Makes sense. I have changed the EGR thermostat TWICE now in the last 2 months without any positive results, today on an 18 mile journey (mainly motorway) engine temp didnt get above 63 degrees, seemed to shoot up to 43 then sit at 50 for a long time before gradually creeping up. Therefore I should probably rule out the EGR thermostat as being the problem.

I changed the main thermostat about 1 month ago too, as that seemed to be the natural progression with this reoccurring fault.

Quote:

Originally Posted by HighlandPete

NOTE: A faulty auto gearbox oil cooler thermostat can do the same, it also can by-pass the main thermostat, and allows cold coolant directly from the bottom of the radiator into the circulating flow.

Oil cooler thermostat is part of the heat exchanger, so a costly repair.

HighlandPete

So I am screwed then - as it sounds like this is the only thing left to do?

One chap mentioned the "Top Hose Thermostat Modification" in a previous post and that worked successfully- as I undertand this is inserting a "Thermostat" into the top hose preventing any Bi-pass situations. I searched and searched for this but couldnt find the spec or DIY on how to do this and with what parts - or is it safe to do versus the "costly" gearbox heat exchanger repair?

Is there anything else I can do / try to diagnose my low coolant temperatures Definitively??